Method of granulating superphosphate



Feb. 18, 1941. M. SHOELD METHOD OF GRANULATING SUPERPHOSPHATE Filed Jun 15, 1938 4 Sheets-Sheet 1 NM m Feb. 18, 1941. s-oE A 2,232,l45

METHOD OF GRANULATING SUPERPHOSPHATE Filed June 15, 1958 4 Sheets-Sheet 2 &brown/go Feb. 18, 1941. M. SHOELD 2,232,145

METHOD OF GRANULATING SUPERPHQSPHATE Filed June 15, 1938 4 Sheets-Sheet 3 rin) l/I, /l

Feb. 18, 1941. SHOELD 2,232,145

METHOD OF GRANULATING SUPERPHOSPHATE Filed June 15, 1938 4 Sheets-Sheet 4 Patented Feb. 18, 1941 UNITED sTAT-:s

p 2,232,45 METHOD or GRANULATING SUPER- OSPHATE 'Mark Shoeld, Baltimore, Md., assignor to The Davison Chemical Corporation, Baltimore, Md.

Application June 15, 1938, Serial No. 213,927

` 1 Claim.

My invention relates to the manufacture of granular superphosphate.

In my co-pending application Serial No.

2l3,925, filed June 15, 1938, I have disclosed a process which involves the addition of dry granular material to the fresh den superphosphate to accurately regulate the character of the material passing'to the conditioning step. such material accurately regulated as to the moisture content passes to a conditioning step where the material is tumbled in a rotary cylinder' to agglomerate' it into granular particles. These particles are then passed to a drier. In the drier the granular particles are subjected to agitation by rotating the drum which comprises the drier and the final product is a granular superphosphate material having encrusted and indurated nodular globoid particles.

In the preferred form of thi process, I use as 20 the dry additional material prior to the conditioning step, classifier dust. That is to say dust which is formed by classifying or screening the granular material as it finally passes from the drier. The large nodules must be broken up, and it is desirable to have a uniform size of particles in the final product. The dust which is formed in this classifying step is returned as dry, fully 'cured superphosphate dust, or as it is called, "classifier dust." This dust is mixed with the fresh den superphosphate in the moisture condition step.

An object of the invention is to disclose processes and apparatus which will permit the formation of substantial uniform size encrusted, indurated nodular globoid particles of superphosphate material with a small percent of HzO in the material passing to the drying step. Thus there is a considerable saving effected in capacity of apparatus and cost of the process.

A further object is to permit utilization of all the classifier dust taken from the product after the final drying by returning all of the classifier dust to the fresh den superphosphate prior to the conditioning. l

Other objects will appear from the ensuing description.

The purpose of this addition was to make it possible to use fresh superphosphate directly from the den and still make it practicable to obtain the necessary regulation of physical condition of the material from the conditioner to the dryer.

The amount of classifier dust added to the feed of the conditioner was approximately 10% of the total feed as cited in the typical example in the disclosure of Serial No. 213,925.

The moisture content of the fresh superphosphate to the conditioner was lo /2%. The material from the conditioner to the dryer also had 5 a moisture content of 10% The granular material right from the unit contained about 5% moisture. Thus the moisture elimination in the dryer-was about 5 /2%.

If the classifier dust content of the feed is in- 10 creased beyond 10% of the amount required for satisfactory regulation, then the total capacity of the dryer drops down. The reason for this is that it requires more than 1o /2% moisture in the material from the conditioner to obtain the required physical condition of the material as it enters the dryer. The amount of water required in the conditioner when more than 10% classifier dust is used is approximately 15% of the extra classifier dust added. Thus if instead of 10% 2 classifier dust is used it means that the moisture content of the material from the conditioner .to 'the dryer is increased 1 /2% or from lo to 12%. The moisture elimination in the dryer in th/is latter case will be 7% instead of the previous 2%.

As the capacity of the dryer is practically a function directly proportional to the moisture elimination, the result is that with 20% classifier dust the capacity of the dryer is only 78% of that with 10% classifier dust.

In the past it has been the practice to dispose of excess classifier dust, not required in the process, by means of mixing it with run of pile regular superphosphate and sell it as such or cut to regular 16% superphosphate.

The amount of classifier dust produced by pneumatic separation is generally around 15 to 20% of the total production. With 10% going back into the process it means that 5% to 10% has to be disposed of separately or otherwise reworked, sacrificing capacity of the granular unit.

With more exact classification, using double screening, to obtain a final product substantially all within the range of minus 10 mesh and plus 20 mesh, by Tyler standard screen analysis, the i amount of classifier dust is increased to about 20 to 30% of the total production.

By means of this invention it is possible to rework up to 30% classifier dust in the granulatin'g unit without sacrifice of any net capacity. As a matter of fact the actual running capacity of the dryer is increased more than 50%.

This is accomplished in the following manner. Instead of using a rotary cylinder for the condimay be discharged by a slat tioning or the material prior to drying. the material is worked' more strenuously. This may be accomplished bymeans of a severe knea'ding action.

By means o! the energetic imeading action it has been found possible to incorporate up to 30% dry-dust in'the fresh den superphosphate and still obtain the desired physical condition of the material as it enters the dryer. r.

In the drawinzs:

Figure 1 illustrates in of apparatus, my process;

Figure 2 iuustrates in cross section another formof apparatus and another method oi' carrying out my process;

Figure 3 form of process and apparatus for carrying out my invention;

Figure 4 illustrates in cross section yet another form of -apparatus and process tor carrying out my invention. i

Referring to Figure to which is delivered other suitable means, 2. There is provided handle 4 at one side of the amount of fresh and one method of carrying'out 1, I have shown a hopper i by a clam shell bucket, or

a gate 3 with an Operating the hopper i for regulatins den superphosphate which conveyor 5.

The slat conveyor 5 discharges the fresh den superphosphate on to a sloping wall 6 of a hopper Located above the sloping wall which may be regulated by means and by which aqueous medium may into the hopper 1. hopper of a valve E, be discharged There is provided another o having classifler dust li therein. In

the bottom of the hopper is located a screw conveyor |2 'driven by a motor !3 through a suitable reduction gearing M, driven by a variable speed transmission M' having a control handle id" mounted thereon. The screw conveyor i 2 discharges classifier dust through a conduit !5' into the hopper 1. A skillful operator can regulate the mixture of classifler dust, fresh den superphosphate and the water so that the material passing out of the hopper 'l has a moisture contentwhich may be approximately 8%%. Ti'is is a lower moisture content than has heretofore been possible. However, by my method I am able to have the material which passes to the conditioning step low in water, thus saving the size of apparatus and necessary heat units to evaporate the final ture content.

From the hopper 'I the mixed classifier dust and fresh den superphosphate pass to a long cylindrical chamber |5 which has set in its walls a series of blades I 6 which lie between a series of blads I'I mounted on a rotary shaft !8. The blades l'i on the shaft iB have their surfaces inclined so that when the shaft s is rotated the material in the chamber |5 is fed forward from the entrance end IS to the discharge end 20. The material in the chamber is subjected to a very severe kneading action. The shaft |8 is driven through reduction gearing 2| coupled to a variaproduct to the desired moisble speed transmission 22 having a control member 23.

The variable speed transmission 22 is coupled to the shaft of an electric motor 24.

Under certain conditions of operation the mixing of the materials in the chamber |5 may .be of such a nature as to cause sufiicient agglomeration of the particles so that they may be readily discharged into a hopper 25 and pass thence cross section one form i illustratesin cross section yet another fresh den superphosphate 6 is a spray 8,

aaaaas ilrough a water-iacketed ohute 26 into a dryer The dryer 21 has its axis inclined to the horizontai. and its high or intake end 28 is provided with-an aperture 29 into which the lower end of thespout 23. projects. Thelower end 30 of the rotary cylindrica dryer 21 discharges on to a chute 3I. the material passing from thence into a receiving' pit 32, from which it may be withdrawn by a cam sheu bucket or other suitable means. The end 30 ot the rotary dryer 21 is covered by an exhaust breeching 33 having a suction fan 34 in communication therewith. There is a hinged flap 35 formed at haust breeching which `bears against the dise' charged dried granular superphosphate and prevents too much leakage of air into the exhaust breeching 33 past the stream of discharging phosphate granules.

to rotate, I

- gearing may be used between the pinion'40 and .the motor el in order to reduce the speed of rotation of the dryer 21. A flre clay lined breeching 42 is provided at the high' end 23 of the dryer. There is an aperture 43 formed in' one wall of the breeching 42 through which projects a burner 44 adapted to burn oil or gas. A bame wall 45 is i'ormed in the interier of the breeching 42 to prevent direct contact of the fiame with the chute 26.

In operation the hot gases pass over the noduies which are in the dryer and remove moisture from them so that the final product has the desired moisture content.

Figure 2. In this form of invention the action on the material in the elongated chamber IS is not such as to properly coagulate particiesof desired size for drying. Under such circumstances it is necessary to have a conditioning step between the chamber I 5 and the dryer 21. The discharge end 20 of the chamber |5 discharges into a hopper me which, through a chute Hil, feeds through an aperture !02 into a rotary cylindrical conditioner os. The rotary cylindrical conditioner !03 is mounted on rings IM which rest on rollers !05 carried by supports me. To rotate the conditioner |03,I have provided a ring gear !01 driven by a pinion !08 mounted'on the shaft of a motor i 09.

The rotary conditioner !03 is mounted with its iongitudinal axis at an angle to the horizontal so that the particles of material passing through the chute o pass from the high end HO of the rotary conditioner I 03 and are discharged at the lower end IH. In their passage through the conditioner the particles are agglomerated to the desired size to permit them to pass to the hopper 25 which feeds through chute 26' to the rotary dryer 21.

In either form of apparatus, Figure 1 or Figure the bottom of the ex- 15 40 An alternate form of the invention is shown in I material from the dryer is maintained at The moisture eiimination in the dryer is therefore 3 /2%. Under standard Operating conditions heretofore, the moisture elimination has been !i In other words. by means o! this invention, the capacity of the dryer is increased about 1.6 times.

Looking at the matter from a somewhat different angle, this invention makes it possible to rework all the classifier dust produced in the process, no matter how severe the classiflcation operation is, without sacrificing any net capacity of the granulating equipment.

Again re-stating it in a somewhat different' manner, as the cost of the granulation is primarily a direct proportional function of the capacity of the granulating equipment, it makes it possible to produce substantially perfectly sized granules without any significant additional cost above that of primary granulation.

In Figure 3, I have shown a somewhat diiierent form o! apparatus which effects a desirable severe kneading action. Here I employ a container 200 in which are mounted plows 20l, pivotally mounted by shafts 202 carried by support arms 203. The support arms 203 are driven by a shaft 204 which is journaled in a support spider 205 mounted on the top o! the container 200.

The shaft 204 has a beveled gear 206 at its top which is driven by a beveled pinion 201 mounted on a shait 208. The shaft 208 is journaled in supports 209 mounted on the support spider 205. A suitable motor, not shown, is adapted to rotate the shaft 208 and cause the plows 20! to revolve around the inside of the container 200, throwing in towards the center the mixed den superphosphate and finely divided dry material or classifier dust. As the material is thrown in towards the center of the container 200, heavy beveled rollers 2|0 pass over the material, crushing and kneading the material on the bottom of the container. These beveled rollers are carried on support shafts 2I2, which are attached to a central shaft 204. The shaft 204 may have a plow 2|4 at its bottom. to prevent accumulation of the material at the center of the apparatus. The p p se of this construction is to throw the material being treated directly in the path o! the heavy beveled rollers 2l0 and to cause the material to be thoroughly and intimately crushed and kneaded.

If water is desired, it may be supplied through a nome 2l5 controlled by a valve 2IS. When the material has been thoroughly mixed and is in the proper condition, there is a sliding gate which may be raised by means of a handle 2|0. Then the inclination of the plows 20l is reversed and the material is discharged outwardly and through the gate 2 ll into a hopper 2|0. 4

From the hopper 2l0 the mixed den superphosphate and classifier dust. which is in the proper condition with the desired low moisture content, is discharged by the screw conveyor 220 which feeds through a conduit 22| into the apel-tute' I02 of the conditioner !00. The screw conveyor 220 is driven by a motor 222 through suitable reduction gearing 223. If deslred, a variable speed transmission 224 may be employed to more accurately regulate the speed of rotation of the screw conveyor 220. In this form of apparatus the operation is somewhat of the batch type in that the initial treatment of the mixture is a batch treatment. There can be, however, a suflicient supply of material in the hopper 2I9 to insure continuous operation of the rest of the process. i

Referring to Figure 4, I have shown a somewhat similar type `of apparatus to that shown in Figure 3. That is to say, I have shown means for obtaining a mixture in a batch operation. Here I have a receptacle 300 mounted on a shalt 30! journaled in supports 302. The shalt 30| passes through the walls of the container 300 and carries a helical blade 303 which is mounted outside and in close proximity to a helical blade 304 which is carried by an interior shaft which passes through the shalt 30l.

The shaft 30! is rotated by means of a gear 306 and the shaft 305 is rotated by a gear 301. These gears 306 and 301 are driven by means of pinions 308 and 309, respectively, mounted on a shaft 3l0 which projects from a reduction gearing 3| l, to which power is supplied by means of a motor 3i2. The ratio of the gearing is such that the interior blades 304 revolve at higher speed than the outer blades 303. A finely divided material, such as classifier dust and den superphosphate, are red to the container 300. Water may be added through a spray nozzle 313 controlled by a valve 3", if desired.

When the batch is properly mixed the container 30 is rotated on the shaft 30l and the batch is dumped into a hopper 315 from which the material is discharged by means of a feed screw 3l6, which discharges through a conduit 3|1 into the opening I02 of a container I03. The shaft 3l8 of the feed screw :s is driven through a variable transmission 3!! coupled to a reduction gearing 320 driven by a motor 32I.

It will be seen that economies in size of apparatus and cost of process are achieved by the processes and apparatus herein described without sacriflcing the quality of the granular superphosphate product.

I claim:

A process of treating den superphosphate to produce a granular superphosphate fertilizer that is in hard dry encrusted and indurated particles having several times the crushing strength of ordinary den superphosphate comprising adding 30% classifier dust to the fresh den superphosphate, adjusting the moisture content oi' the mixture to approximately ti subjectlng the mixture to a severe kneading action, forming the mixture into agglomerated partlcles, tumbling the agglomerated particles in a zone oi' hot gases until the moisture content of the particies is reduced to substantially 5% and then dlscharging the particles from the drying zone.

MARK SHOELD. 

